Home gaussmeter with filter-integrator circuit for measuring elf radiation

Abstract

A meter (10) for measuring extremely-low-frequency radiation includes a coil circuit (22) whose output is filtered by a sharp-cut-off high-pass filter (24) to pass standard house-current frequencies but suppress the frequency components that would predominate as a result of movement of the meter with respect to the earth's magnetic field. An integrator (26) compensates for the frequency response of the coil circuit (22), an RMS circuit (35) converts the signal to its root-mean-square value, and a display circuit (28) provides a display determined by the resultant signal.

We claim: 
     
       1. A meter for measuring extremely-low-frequency electromagnetic fields comprising: A) a coil that produces a coil voltage in response to varying magnetic fields;   B) a filter-integrator circuit connected to receive the coil voltage as its input and having as its transfer function the product of those of a high-pass filter and an integrator, the high-pass filter having a cut-off frequency below 60 Hz and an attenuation at 10 Hz at least 20 db greater than its attenuation at 60 Hz; and   C) a display circuit responsive to the output of the filter-integrator circuit for generating a visual indication thereof.   
     
     
       2. A meter as defined in claim 1 wherein the display circuit includes discrete display devices on which it generates a visual indication in an analog form. 
     
     
       3. A meter as defined in claim 2 wherein the spacing of the devices in the discrete-device analog display is substantially logarithmic. 
     
     
       4. A meter as defined in claim 1 further including an RMS circuit interposed between the filter-integration circuit and the display circuit so as to apply to the display circuit an RMS output representative of the root-mean-square value of the output of the filter-integrator circuit.